1. Field of the Invention
The present invention relates to a system and method for synchronizing remote generators. More particularly, but not by way of limitation, the present invention relates to a system for synchronizing a generator to a synchronous bus without the need to have the synchronous bus available at the generator.
2. Background of the Invention
Generally speaking, a power plant uses generators rotated by steam, water, or an engine to produce electrical energy in the form of three-phase alternating current of a fixed voltage and a fixed frequency. Electricity so produced is then delivered to consumers through a network of transformers and transmission lines often referred to as a power distribution grid, or just the “grid.” Within the grid of a single utility company, power generation will often be distributed among several power plants to reduce distribution costs and to improve the reliability of the system. With multiple generators operating, a customer need not lose electrical power simply because a single generator has been taken off-line.
In addition, adjoining utility companies often interconnect their individual grids to create a larger grid. In such an arrangement, if one company under-produces power, it may purchase power from its neighboring company rather than interrupt service. At the extreme, virtually every utility company in a country may be connected to its neighboring grids to create a national power grid. As a result, an under-producing company can look nearly anywhere in the country to find an overproducing company from which to purchase power.
As is well known in the art, a generator can only be connected to a common electrical bus, or grid, if turning in synchronization with other generators already on the grid. Synchronization requires that the generators are producing alternating current at the same frequency, and that the outputs of the generators are in phase with one another. If both conditions are not met, extremely large electrical currents will flow through the generators, potentially tripping circuit breakers within the network, or even damaging equipment. If a national grid is in place, ideally every generator on the grid, across the entire country, should be turning in synchronization.
Typically, before a generator is placed on line, electrical power from the grid is present at the power plant, right up to the contacts that tie the generator to the grid. Thus, the generator may be synchronized to the power already present on the grid prior to making the connection to the bus. Unfortunately, if power is not already present at the power plant, there is presently no method for synchronizing the generator to active portions of the grid. For example, after a disaster, i.e. a hurricane, tornado, flood, earthquake, or the like, substantial portions of a grid may be damaged and a generator within a damaged area may be isolated from the rest of the grid. While such a generator could be placed on-line to supply its local area with electricity, sections of the grid powered by the generator can not be reconnected to the grid without first taking the generator back off-line since the generator would be operating asynchronous to the grid. In many instances, a utility will simply not place a generator back on line until synchronization is possible. As a result, customers may be without electricity for undue periods simply because grid power has not been restored to a nearby power plant. If remote synchronization was available, the power cold be restored to such areas as local repairs were made.
In addition to the problem of synchronizing a generator to a bus at startup, maintaining synchronization while running is also of concern. Unfortunately, it is presently impossible to ascertain with certainty whether or not the generator remains in synchronization with the bus. Obviously, if power is monitored at the power plant, the wave form will be most influenced by the local generator, or generators, rather than power on the bus from other sources. Thus, frequency and phase regulation are more likely due to the tendency of the generator to act as a motor when under-producing and the restrictive load placed on the generator when over-producing than to presently used synchronization systems.
Once a generator is on-line, the mechanical input is typically adjusted to maintain a rate of generation roughly equal to the expected usage. Typically, this level of generation is scheduled. As a result, under demand results in overgeneration which translates into losses for the generating company. In some instances, overgeneration can actually push the generator out of synchronization with the bus, causing a phenomenon known as inadvertent interchange wherein electrical power is unintentionally transferred from one utility company to another over the grid. Unfortunately, at the power plant, the power losses associated with overgeneration are difficult to distinguish from legitimate load.
One method to prevent over or under generation is to measure actual usage, in real time, for each consumer. Such a method requires a telemetric electric meter at each residence and business served by the utility. Even if such meters were already in place, presently there is no infrastructure for sending such an enormous amount of information back to the power plants in a timely manner to allow meaningful control of the generators. Another possibility would be to measure power transfer at each point where the utility ties to another grid. While this method would reduce the incidence of inadvertent interchange, it does not distinguish between losses caused by lapses in synchronization versus dynamic changes in the actual loads both on the local grid and across the boundaries with neighboring grids.
It is also well known in the art that a fault in a power transmission line causes a disturbance on the power line. Such disturbances can be observed with proper equipment even miles away from the fault. Capturing such faults with a power line monitor is well known in the art. In fact, such disturbances may be captured at multiple locations with multiple power line monitors. Unfortunately, while the existence of the fault may be indicated, there is presently no means for determining the location of the fault with such monitors. If, however, real time clocks in two are more monitors were precisely synchronized, it would be possible to log the time of arrival of a disturbance at each monitor and calculate the position of the fault in the transmission line by the differences in the times of arrival. As will be appreciated by those skilled in the art, since disturbances travel at the speed of light along the transmission line, even minute differences in the real time clocks of different monitors would result in unacceptable errors in the calculation of a location.
It is thus an object of the present invention to provide a system and method for synchronizing a generator to a bus even when power from the bus is not available at the generator.
It is a further object of the present invention to provide a system and method for maintaining synchronization of two or more interconnected generators.
It is still a further object of the present invention to provide a system and method for recording the precise time of the arrival of a power line disturbance such that, when such a time is recorded at two or more locations, a distance to the source of the disturbance may be calculated.